MOSCOW (Bloomberg) - Russian opposition leader Alexey Navalny called on his supporters to attend a rally in the Volga city of Nizhny Novgorod after police detained him in Moscow as he prepared to travel to the event.

"I can't come to today's meeting because the Kremlin is really afraid of this event we're planning," Mr Navalny said on Friday (Sept 29) in a video message posted on his Twitter account. "Let them be afraid, but I call on you to turn up anyway."

Police in Moscow said they arrested Mr Navalny for repeatedly calling for unauthorised rallies, according to state-run Tass news service.

In Nizhny Novgorod, about 400 kilometres south-east of Moscow, police dismantled a stage set up for Mr Navalny's rally, Ekho Moskvy radio reported.

The anti-corruption activist has announced his candidacy for March 2018 presidential elections that would almost certainly pit him against President Vladimir Putin, who's likely to seek a record fourth term.

Officials say Mr Navalny is barred from running because of a fraud conviction that he's dismissed as politically motivated.

Mr Navalny has drawn thousands of people to a series of campaign rallies in cities across Russia recently, after inspiring the largest anti-government protests for at least five years in March.

Mr Navalny, who almost forced a run-off against a Putin ally in the 2013 Moscow mayoral election, came to prominence as a key organiser of mass protests that erupted over alleged ballot-rigging in 2011-2012.

The protests were the biggest since Mr Putin came to power almost two decades ago.